1. Field of the Invention
This invention relates to a flexible structure including electronic and/or electromagnetic devices and, in particular, to a contact structure for electrically connecting the devices so that electrical contact between the devices is maintained when the flexible structure is bent or otherwise deformed.
2. Related Art
There are a wide variety of applications that can make use of a flexible structure including electronic and/or electromagnetic devices, the devices being used for information input and output to and from the flexible structure, information processing and information storage. One example of such a flexible structure is a flexible identification card.
An identification card, as defined by the International Standards Organization (ISO) in ISO 7810, is "[a] card identifying its bearer and issuer which may carry data required as input for the intended use of the card and for transactions based thereon." Identification cards can have one of three nominal sizes (as specified in ISO 7810): 1) 3.370 inch (85.60 mm) width, 2.125 inch (53.98 mm) height, 0.030 inch (0.76 mm) thickness; 2) 4.134 inch (105 mm) width, 2.913 inch (74 mm) height, 0.030 inch (0.76 mm) thickness; 3) 4.921 inch (125 mm) width, 3.465 inch (88 mm) height, 0.030 inch (0.76 mm) thickness.
Some identification cards include an integrated circuit and are known as "integrated circuit cards" or "Smart Cards." More generally, herein, "Smart Card" refers to any portable card-like device which includes one or more electronic components, i.e., active components such as integrated circuits, transistors and diodes, and passive components such as resistors, capacitors and inductors. The integrated circuits can be formed on an integrated circuit chip and/or printed circuit board that is, in turn, attached to the main body of the Smart Card. Smart Cards can be used for a wide variety of applications such as prepaid "debit" cards (e.g., phone cards, transit passes, electronic purse), subscriber cards (e.g., bank ATM cards, credit cards, point-of-sale cards), loyalty scheme cards (e.g., frequent flier cards), security access and identification cards, health insurance and service cards (with optional protected memory), GSM (global system management for European Cellular Phones) cards and encryption/decryption cards.
Smart Cards are used with a reader/writer that includes an interface ("external interface") that is used to transmit information to or from the Smart Card. Some Smart Cards include electrical contacts which are used to make electrical connection between electrical circuitry on or within the Smart Card and the external interface. Other Smart Cards do not include electrical contacts and accomplish the transfer of information to and from the Smart Card through another means such as, for example, an inductive coil formed in or on the Smart Card that is used in combination with an external interface that produces and responds to an electromagnetic field, i.e., electromagnetic contact-less Smart Cards. Other types of contact-less cards use electro-static or capacitive coupling to accomplish the transfer of data and instructions to and from the card.
In Smart Cards (and other structures such as printed circuit boards, for example) including two or more electronic or electromagnetic devices, it is generally necessary or desirable to electrically interconnect the devices. Typically, in Smart Cards, this is done within the main body of the Smart Card. Electrical interconnection is made between electrical contacts on the respective devices, e.g., electrically conductive traces on a printed circuit board, electrically conductive bond pads on an integrated circuit chip, terminal points of an inductive coil.
In some previous flexible structures including two or more electronic or electromagnetic devices, electrical interconnection has been made between the devices by soldering or welding the respective electrical contacts together, or by attaching the respective electrical contacts with an electrically conductive adhesive. However, when the flexible structure is bent, the relatively rigid (as compared to the flexible structure) solder, weld or adhesive can break, resulting in failure or degradation of the electrical interconnection. Further, soldering or welding the respective electrical contacts together is a difficult task since it is difficult to position the soldering or welding equipment within a cavity formed in the main body of the card for placing one of the devices, e.g., an integrated circuit module. Additionally, most flexible Smart Cards (as well as many other flexible structures) are made of low temperature plastic which undesirably melts at the temperatures necessary for soldering, welding or heating an adhesive.
In other previous flexible structures including two or more electronic or electromagnetic devices, electrical interconnection has been made by forming holes through the main body of the card, the holes extending between the respective electrical contacts of the devices, then inserting copper "studs" into the holes which are attached at either end to the respective electrical contacts by soldering, welding or use of an electrically conductive adhesive. However, when the flexible structure bends, the rigid copper studs do not, so that, frequently, one or more of the copper studs break away from one or both of the electrical contacts, thereby breaking the electrical interconnection between the devices.